For years, the U.S. Drug Enforcement Administration has engaged in a questionable use of thousands of informants.

The DEA has used airline employees, parcel services workers and even staff at other government agencies, such as the Transportation Safety Administration and Amtrak, as its informants, in violation of Justice Department policies.

According to a recent audit from the Justice Department’s Office of the Inspector General, the DEA amassed an army of more than 18,000 informants between October 2010 and October 2015. Informants are offered cash rewards of up to $500,000 or 25 percent of successful cash seizures, whichever is less, and the DEA made $237 million in payments to more than 9,500 sources during this period.

The DEA uses these informants to get around pesky privacy protections like the Fourth Amendment and obtain traveler information that private companies would not hand over without a subpoena.

While ostensibly seeking illegal drugs, which are a relatively rare find, or, more commonly, the proceeds of drug transactions, such searches also result in seizures of cash from innocent people, not to mention the harassment of countless other passengers who are not carrying drugs or large sums of cash. Moreover, usually, agents seize large sums of cash from travelers and then send them on their way without charging them with any crime.

“The deficiencies we identified in this audit raise significant concerns about the adequacy of the current policies, procedures and oversight associated with the DEA’s management of its Confidential Source Program,” the OIG’s report concluded.

Unlike other intelligence agencies, “the DEA does not independently validate the credibility of sources used for intelligence programs or the accuracy of the information they provide.” This led to the use of sources such as one who was continually used — and paid, to the tune of more than $460,000 — despite his “deactivation” because he “previously provided false testimony in trials in depositions.”

OIG “found the DEA did not appropriately track all confidential source activity, did not document proper justifications for all source payments and, at times, did not adequately safeguard traveler information,” as tips were often sent over unsecure email or text to agents’ private accounts.

There is no way to know if the program is even effective, since the DEA only keeps track of situations in which a search leads to an arrest or a seizure, and even then only limited information. As “The Economist” put it, “For every successful seizure, there might have been 10 passengers inconvenienced by a search. Or 100. Or 1,000.” What is most troubling is that the DEA doesn’t seem to care if the program is effective at preventing illegal activity — as long as it gets to seize a bunch of money in the process.

The DEA and other law enforcement agencies face skewed priorities when they can search and seize property — and then keep the proceeds — without so much as probable cause or a warrant, much less a conviction. The DEA’s Confidential Source Program does an end run around the Fourth Amendment and facilitates such abuses, with no assurances that it is effective or well managed. It should be eliminated immediately to prevent further waste of taxpayers’ dollars and abuses of travelers’ constitutional rights.

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